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Recovery of hyperplastic responsiveness in rat liver after dosing with the peroxisome proliferator methylclofenapate
J A Styles1, M D Kelly, C R Elcombe
1Imperial Chemical Industries plc, Central Toxicology Laboratory, Alderley Park, Macclesfield, Cheshire UK.
Abstract:
Methylclofenapate (MCP) was administered daily by gavage (25 mg/kg) for 7 days to groups of adult male rats. Dosing was interrupted for 28, 35, 56, 70 or 84 days and then resumed (25 mg/kg by gavage at 0 and 24 h). During the second period of dosing animals were killed in groups of three at 6, 12, 18, 24, 30, 36, 42 and 48 h after the resumption of dosing. Hepatocytes in S-phase, labelled with bromodeoxy-uridine, were analysed by flow cytometry, cell sorting and microscopy. It was observed that total S-phase activity was just significantly elevated (approximately 20% of maximum) over corn oil controls after an interval of 28 days between initial and subsequent dosing periods. After an interval of 35 days total S-phase activity was approximately 65% of maximum, and full hyperplastic responsiveness, equal to that observed in naive animals given MCP, was detected after interruptions in dosing of 56, 70 and 84 days. The recovery of S-phase responsiveness during the interruptions in dosing was accompanied by an increase in the proportion of 2 X 2N hepatocytes from approximately 10% in animals dosed continuously with MCP, to approximately 11.4% after 28 days interruption, 17% after 35 days and control levels (approximately 20%) after 56, 70 and 84 days. Irrespective of the magnitude of the hyperplasia elicited by the second period of dosing with MCP, the proportion of 2 X 2N cells was reduced to the same levels as those observed in animals dosed continuously with MCP (approximately 10%). Very low S-phase activity (0.05%) was observed in animals dosed continuously with MCP, this level of activity being similar to that in animals given corn oil continuously.
Insights
Methylclofenapate (MCP) treatment requires a minimum 56-day interruption for full liver cell regeneration. Shorter breaks (28-35 days) show partial recovery of S-phase activity and 2X2N hepatocytes.
Area of Science:
- Hepatology
- Toxicology
- Cell Biology
Background:
- Methylclofenapate (MCP) is a compound known to induce liver hyperplasia.
- Understanding the recovery kinetics of liver cell proliferation after drug withdrawal is crucial for assessing long-term safety and efficacy.
Purpose of the Study:
- To investigate the impact of varying interruption durations on the regenerative capacity of hepatocytes following methylclofenapate (MCP) administration.
- To quantify the recovery of S-phase activity and the proportion of 2X2N hepatocytes after different periods of MCP dosing cessation.
Main Methods:
- Adult male rats were administered MCP (25 mg/kg) daily for 7 days.
- Dosing was interrupted for 28, 35, 56, 70, or 84 days before resuming MCP administration.
- Hepatocyte proliferation (S-phase activity) and 2X2N cell populations were analyzed using flow cytometry and microscopy after dose resumption.
Main Results:
- Significant elevation in S-phase activity was observed after 28 days (20% of max) and 35 days (65% of max) of interruption.
- Full hyperplastic responsiveness, comparable to naive animals, was achieved after 56, 70, and 84-day interruptions.
- The proportion of 2X2N hepatocytes increased with longer interruption periods, returning to control levels after 56 days or more.
Conclusions:
- A minimum interruption of 56 days is required for complete recovery of methylclofenapate-induced liver hyperplasia.
- The recovery of proliferative capacity is dose- and time-dependent, with longer breaks facilitating full regeneration.
- The proportion of 2X2N hepatocytes serves as a reliable indicator of liver regeneration status after drug-induced hyperplasia.